It's very easy to create an account on the following portal and add money online: https://www.so-happy.fr/
You just need to know your badge number. Note that this is NOT the CEA badge number, but the number that is on the printed receipt you get when you pay. The receipts are not printed by default any longer: you have to ask the cashier to print the receipt, and bring this receipt back with you.
The web site is available in English, if your browser language is set to English! You can also change the language in the COMPTE (FR) or MY ACCOUNT (EN) settings' page.
Try to access the English version of the SoHappy web site, or ask a French speaking colleague to help you. You can then easily manage your account settings (and select the English language), add money (remotely) and specify when you want to receive a mail telling you that there is not enough money left on your account.